Brain Imaging Flashcards
Structural Imaging
provides detailed images of the anatomical structures of the brain or body. It helps visualize the size, shape, and position of tissues and organs. This type of imaging is typically used to diagnose injuries, tumors, structural abnormalities, or degenerative conditions.
Functional Imaging
focuses on capturing physiological activity within tissues, showing how organs work in real-time. It helps assess brain activity, metabolism, or blood flow, providing insights into how well the brain or other organs are functioning.
Structural imaging provides details on the anatomy of the brain or body.
Functional imaging shows real-time activity or physiological processes in organs or tissues.
Structural typically has higher spatial resolution (better for detailed anatomy).
Functional often emphasizes temporal resolution (tracking changes over time).
Risks of Xray
Exposure to radiation, the amount used in most medical applications is low.
However, repeated exposure or high doses (e.g., in certain treatments) can pose health risks
X-ray
form of electromagnetic radiation with a wavelength shorter than that of visible light, making it capable of penetrating solid objects, including human tissue
absorbed at different rates by different tissues.
Advantages of X-ray
X-rays are fast, non-invasive, and relatively inexpensive compared to other imaging techniques like MRI or CT.
Computed Tomography (CT Scan)
medical imaging procedure that uses X-rays and computer processing to create detailed cross-sectional images of the bod
Instead of taking strong xray, take bunch of weaker xray in different angles. Computer take all these 2d image and does “Reconstruction” to build a 3d image of what is going on in the brain
Cerebral angiography
medical imaging technique used to visualize the blood vessels in the brain. It helps doctors evaluate abnormalities in the brain’s vascular system, such as aneurysms and blockages that could lead to strokes.
Process of Cerebral Angiography
an iodine-based contrast agent is injected into the brain’s blood vessels–> visible on X-ray images–> X-rays pass through, the iodine absorbs them differently–> a detailed and vivid map of the brain’s circulatory system
Disadvantage of a CT Scan
Can’t differentiate white and gray matter→ cant tell if you have a tumor growing your brain because tumor is tissue
Tissue and fluid seen in the picture but it is not as clear as an MRI
Common use of CT Scan
diagnose conditions like fractures, tumors, internal bleeding, and other internal injuries, offering faster and more detailed results than traditional X-rays.
Magnetic Resonance Imaging (MRI)
non-invasive medical imaging technique that uses strong magnetic fields, radiofrequency pulses, and a computer to produce detailed images of internal structures, both tissue and fluid can be seen
Unlike X-rays or CT scans, MRI does not use ionizing radiation. Instead, it exploits the alignment of hydrogen protons in the body’s water molecules when exposed to a magnetic field.
Overlay Plot
graphical representation that combines multiple datasets on the same axes, allowing for the comparison of patterns, trends, or distributions across different groups
useful for visualizing similarities and differences in brain symptoms among individuals with similar conditions.
Steps for an MRI Scan
- aligning all the protons in the body using a strong magnetic field, which begins even before the scan starts
- momentarily disrupts this alignment, producing a loud sound; as the protons realign, they release energy, which is used to create images.
- MRI machine measures the radiofrequency (RF) signals generated during this relaxation process to produce detailed images of the internal structures.
Diffusion Tensor Imaging (DTI)
A variant of MRI technique used to study the diffusion of water molecules in biological tissues, particularly in the brain. It provides information about the orientation and integrity of white matter tracts, allowing researchers and clinicians to visualize and analyze brain connectivity.
DTI & White Matter Impairments
can detect subtle changes in white matter that may not be visible through traditional MRI techniques.
Autism and White Matter Connections
DTI studies have shown differences in white matter connectivity compared to neurotypical individuals. These differences may relate to the neural pathways involved in social interaction, communication, and sensory processing, contributing to the characteristic symptoms of autism
Electroencephalography (EEG)
a test that measures electrical activity in the brain
picks up changes and voltage in our brain (wavelengths)
Main diagnostic tool for epilepsy even if the person is not having a seizure
Positron Emission Tomography (PET)
an imaging test that can help reveal the metabolic or biochemical function of your tissues and organs
PET
Radioactive cocaine
find radioactivity where you can find dopamine
PET
Heatmap
cocaine acts really strongly on basal ganglia; basically if glucose, it goes to the part of brain where glucose is
PET
Mean difference images
Control group vs experimental: noise vs no noise
No noise is the baseline measurement
Stimulation condition minus control condition = mean difference
Take individual difference images and make an average of this averages
PET
Psychlotron
makes this radioactive molecules (disadvantage: it decays)
Can’t just keep a jar full of radioactive water or sugar, extremely expensive
Potential problems of PET
Very expensive (need the radioactive molecule)
* Temporally slow
* Poor spatial resolution
Advantages of PET
- Useful for looking at specific systems (e.g. DA) or proteins (tau- creates neurofibulla)
- Useful for looking at lifespan/condition changes (e.g. stroke, maybe CTE?)
- Check function over time(brain changes across lifespan)
heatmap became cooler→ dopamine system becomes weaker and it declines
Addiction and Dopamine
fewer dopamine system function compared to normal one
dopamine D2 receptors decreased by addiction
Functional MRI (fMRI)
an imaging scan that shows activity in specific areas of the brain
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fMRI vs PET
In fMRI, the source of contrast is intrinsic, whereas in PET an extrinsic contrast agent is used.
BOLD response
Blood-oxygen-level dependent (BOLD) response: changes in local oxygenation of cerebral blood flow can be detected.
Hemodynamic response
a homeostatic process that replenishes the nutrients used by biological tissues by adjusting blood flow to areas of focal activity.
movement= Increase in oxygenated blood in an area
mental process at 0 activity occurs in brain- delayed response increase in oxygen at that part of brain
Bold response and astrocytes
Astrocytes have receptors, usually for glutamate→ lead to intracellular calcium
Triggers blood vessels to dilate so O2 should go in there→ calcium mediated response
Paired Image Subtraction
(same idea with mean image difference)
Real importance to research design- quality of your controls depends on the quality of your results
Can’t tell us how activity changes as a function with paired image subtraction
Event-related fMRI
Presenting many of this events– do task over and over
Each individual exposure is a little diff and then average it all out
Money version of marshmallow task
Has many of its own challenges (e.g. boredom!)
Problems with interpreting fMRI studies (1)
- Spatial averaging- epiphenomena- signal doesn’t really truly represent any of the original signals
- Spatial resolution- 1 mm neurons- 13 million neurons in it- hard to say what we are actually seeing
- Temporal resolution- couple of seconds
- Not necessarily necessity- brain activity doesn’t tell you how essential it is for the task, you dont see how IMPORTANT the activity is
- Focus on increases in activity= increase thought = increase bold but negative correlations do matter, decrease activity/ decrease BOLD is important too
Problems with interpreting fMRI studies (2)
- Regional hemodynamics- some diff regions may have slightly diff hemodynamic responses
- Confounds: anxiety, boredom
- Confounds: drugs
- Anticipatory hemodynamics- brain gets clever after u repeat task over and over→ oxygenated blood releases first before u actually need it –problem for data analysis (changed curve)
- Reliability- replication crisis
- Statistics- significant P value→ how much observation is real
each voxel is a significant, there are millions of voxel
5% yield positive
statistics
Bonferroni correction
more conservative estimate
